The present invention is directed to a process for the manufacture of methyl limonitrile. Methyl limonitrile is a mixture of 3,7-dimethyl-2,6-nonadiene nitrile (compound A), 7-methyl-3-methylene-6-nonene nitrile (compound B) and 3,7-dimethyl-3,6-nonadiene nitrile (compound C).
The process according to the invention comprises the step of reacting 6-methyl-5-octen-2-one (6-ethyl-5-hepten-2-one; EH) with cyano acetic acid and removing water and carbon dioxide, wherein the reaction and the removal of water and carbon dioxide are performed in the presence of a base and a co-base and in an organic solvent as shown in FIG. 1.
There is an increasing demand of substituting geranylnitrile by another fragrance, which does not have the toxicological disadvantages of geranylnitrile.
It is already known that methyl limonitrile, a mixture of 3,7-dimethyl-2,6-nonadiene nitrile (compound A), 7-methyl-3-methylene-6-nonene nitrile (compound B) and 3,7-dimethyl-3,6-nonadiene nitrile (compound C), wherein the amount of 7-methyl-3-methylene-6-nonene nitrile and 3,7-dimethyl-3,6-nonadiene nitrile in the mixture is in the range of from 10 to 30 weight-%, based on the total weight of the mixture, does have similar olfactive properties as geranylnitrile.
This especially applies to methyl limonitrile, wherein
the ratio of compound A (3,7-dimethyl-2,6-nonadiene nitrile) in methyl limonitrile is in the range of 60 to 90 norm-% (preferably 70 to 85 norm-%, more preferably 76 to 83 norm-%, most preferably around 80 norm-%),
the ratio of compound B (7-methyl-3-methylene-6-nonene nitrile) is in the range of 0 to 10 norm-% (preferably 0 to 5 norm-%, more preferably 0 to 2 norm-%, most preferably around 0 norm-%), and
the ratio of compound C (3,7-dimethyl-3,6-nonadiene nitrile) in methyl limonitrile is in the range of from 10 to 30 norm-% (preferably 15 to 25 norm-%, more preferably 17 to 22 norm-%, most preferably around 20 norm-%), all based on the amount of compounds A, B and C together, where the ratios of A, B and C given in norm-% sum up to a total of 100 norm-%,and the total amount of methyl limonitrile in the mixture, i.e. the purity, is 95-100 area-% (preferably 97-100 area-%, more preferably 98-100 area-%) as determined by gas chromatography (GC), whereby the conditions for measurement are chosen in a way that all 10 stereoisomers (see FIG. 2) show distinct peaks in the gas chromatogram.
To further illustrate the meaning of “norm-%” an example is given:
In case there is a process product with a purity of methyl limonitrile of 95 area-% and with an amount of compound A of 80 norm-% (A: (A+B+C)=80%), an amount of compound B of 0 norm-% and an amount of compound C of 20 norm-%, that in fact means that the amount of compound A in the process product is 76 area-% (0.95×80%), the amount of compound B in the process product is 0 area-% and the amount of compound C in the process product is 19 area-% (0.95×20%), based on the total weight of the process product.
Such a product is already sold by Givaudan under the tradename “lemonile”. Lemonile is a mixture of 3,7-dimethyl-2,6-nonadiene nitrile, 7-methyl-3-methylene-6-nonene nitrile and 3,7-dimethyl-3,6-nonadiene nitrile, wherein the ratio 3,7-dimethyl-2,6-nonadiene nitrile:7-methyl-3-methylene-6-nonene nitrile:3,7-dimethyl-3,6-nonadiene nitrile=80:0:20 with a purity of >98 area-%.
Furthermore there is also a mixture of 3,7-dimethyl-2,6-nonadiene nitrile (compound A), 7-methyl-3-methylene-6-nonene nitrile (compound B) and 3,7-dimethyl-3,6-nonadiene nitrile (compound C) disclosed by BASF in WO 2009/013199 (see WO 2009/013199: page 12, line 33-39), wherein the total amount of B and C is in the range of 0.01 to 10 weight-%, based on the amount of A (in the following called “mixture according to WO 2009/013199”). In case, however, cyano acetic acid and EH were used as starting materials the reaction time was very long (23 hours, see WO 2009/013199: example 1—page 17, line 14-20: (1+7+12+3) hours; example 2—page 18, line 14-20: (1+7+12+3) hours) thus making the process not very attractive. Further disadvantages of this process are the low yields.
At present no process is known to manufacture such a product in an efficient and economic way at industrial scale.